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+//===- ARMDisassembler.cpp - Disassembler for ARM/Thumb ISA -----*- C++ -*-===//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is part of the ARM Disassembler.
+// It contains code to implement the public interfaces of ARMDisassembler and
+// ThumbDisassembler, both of which are instances of MCDisassembler.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "arm-disassembler"
+
+#include "ARMDisassembler.h"
+#include "ARMDisassemblerCore.h"
+
+#include "llvm/MC/EDInstInfo.h"
+#include "llvm/MC/MCInst.h"
+#include "llvm/Target/TargetRegistry.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/MemoryObject.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
+
+/// ARMGenDecoderTables.inc - ARMDecoderTables.inc is tblgen'ed from
+/// ARMDecoderEmitter.cpp TableGen backend. It contains:
+///
+/// o Mappings from opcode to ARM/Thumb instruction format
+///
+/// o static uint16_t decodeInstruction(uint32_t insn) - the decoding function
+/// for an ARM instruction.
+///
+/// o static uint16_t decodeThumbInstruction(field_t insn) - the decoding
+/// function for a Thumb instruction.
+///
+#include "../ARMGenDecoderTables.inc"
+
+#include "../ARMGenEDInfo.inc"
+
+using namespace llvm;
+
+/// showBitVector - Use the raw_ostream to log a diagnostic message describing
+/// the inidividual bits of the instruction.
+///
+static inline void showBitVector(raw_ostream &os, const uint32_t &insn) {
+ // Split the bit position markers into more than one lines to fit 80 columns.
+ os << " 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11"
+ << " 10 9 8 7 6 5 4 3 2 1 0 \n";
+ os << "---------------------------------------------------------------"
+ << "----------------------------------\n";
+ os << '|';
+ for (unsigned i = 32; i != 0; --i) {
+ if (insn >> (i - 1) & 0x01)
+ os << " 1";
+ else
+ os << " 0";
+ os << (i%4 == 1 ? '|' : ':');
+ }
+ os << '\n';
+ // Split the bit position markers into more than one lines to fit 80 columns.
+ os << "---------------------------------------------------------------"
+ << "----------------------------------\n";
+ os << '\n';
+}
+
+/// decodeARMInstruction is a decorator function which tries special cases of
+/// instruction matching before calling the auto-generated decoder function.
+static unsigned decodeARMInstruction(uint32_t &insn) {
+ if (slice(insn, 31, 28) == 15)
+ goto AutoGenedDecoder;
+
+ // Special case processing, if any, goes here....
+
+ // LLVM combines the offset mode of A8.6.197 & A8.6.198 into STRB.
+ // The insufficient encoding information of the combined instruction confuses
+ // the decoder wrt BFC/BFI. Therefore, we try to recover here.
+ // For BFC, Inst{27-21} = 0b0111110 & Inst{6-0} = 0b0011111.
+ // For BFI, Inst{27-21} = 0b0111110 & Inst{6-4} = 0b001 & Inst{3-0} =! 0b1111.
+ if (slice(insn, 27, 21) == 0x3e && slice(insn, 6, 4) == 1) {
+ if (slice(insn, 3, 0) == 15)
+ return ARM::BFC;
+ else
+ return ARM::BFI;
+ }
+
+ // Ditto for ADDSrs, which is a super-instruction for A8.6.7 & A8.6.8.
+ // As a result, the decoder fails to decode UMULL properly.
+ if (slice(insn, 27, 21) == 0x04 && slice(insn, 7, 4) == 9) {
+ return ARM::UMULL;
+ }
+
+ // Ditto for STR_PRE, which is a super-instruction for A8.6.194 & A8.6.195.
+ // As a result, the decoder fails to decode SBFX properly.
+ if (slice(insn, 27, 21) == 0x3d && slice(insn, 6, 4) == 5)
+ return ARM::SBFX;
+
+ // And STRB_PRE, which is a super-instruction for A8.6.197 & A8.6.198.
+ // As a result, the decoder fails to decode UBFX properly.
+ if (slice(insn, 27, 21) == 0x3f && slice(insn, 6, 4) == 5)
+ return ARM::UBFX;
+
+ // Ditto for STRT, which is a super-instruction for A8.6.210 Encoding A1 & A2.
+ // As a result, the decoder fails to deocode SSAT properly.
+ if (slice(insn, 27, 21) == 0x35 && slice(insn, 5, 4) == 1)
+ return slice(insn, 6, 6) == 0 ? ARM::SSATlsl : ARM::SSATasr;
+
+ // Ditto for RSCrs, which is a super-instruction for A8.6.146 & A8.6.147.
+ // As a result, the decoder fails to decode STRHT/LDRHT/LDRSHT/LDRSBT.
+ if (slice(insn, 27, 24) == 0) {
+ switch (slice(insn, 21, 20)) {
+ case 2:
+ switch (slice(insn, 7, 4)) {
+ case 11:
+ return ARM::STRHT;
+ default:
+ break; // fallthrough
+ }
+ break;
+ case 3:
+ switch (slice(insn, 7, 4)) {
+ case 11:
+ return ARM::LDRHT;
+ case 13:
+ return ARM::LDRSBT;
+ case 15:
+ return ARM::LDRSHT;
+ default:
+ break; // fallthrough
+ }
+ break;
+ default:
+ break; // fallthrough
+ }
+ }
+
+ // Ditto for SBCrs, which is a super-instruction for A8.6.152 & A8.6.153.
+ // As a result, the decoder fails to decode STRH_Post/LDRD_POST/STRD_POST
+ // properly.
+ if (slice(insn, 27, 25) == 0 && slice(insn, 20, 20) == 0) {
+ unsigned PW = slice(insn, 24, 24) << 1 | slice(insn, 21, 21);
+ switch (slice(insn, 7, 4)) {
+ case 11:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::STRH;
+ case 3: // Pre-indexed
+ return ARM::STRH_PRE;
+ case 0: // Post-indexed
+ return ARM::STRH_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ case 13:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::LDRD;
+ case 3: // Pre-indexed
+ return ARM::LDRD_PRE;
+ case 0: // Post-indexed
+ return ARM::LDRD_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ case 15:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::STRD;
+ case 3: // Pre-indexed
+ return ARM::STRD_PRE;
+ case 0: // Post-indexed
+ return ARM::STRD_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ default:
+ break; // fallthrough
+ }
+ }
+
+ // Ditto for SBCSSrs, which is a super-instruction for A8.6.152 & A8.6.153.
+ // As a result, the decoder fails to decode LDRH_POST/LDRSB_POST/LDRSH_POST
+ // properly.
+ if (slice(insn, 27, 25) == 0 && slice(insn, 20, 20) == 1) {
+ unsigned PW = slice(insn, 24, 24) << 1 | slice(insn, 21, 21);
+ switch (slice(insn, 7, 4)) {
+ case 11:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::LDRH;
+ case 3: // Pre-indexed
+ return ARM::LDRH_PRE;
+ case 0: // Post-indexed
+ return ARM::LDRH_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ case 13:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::LDRSB;
+ case 3: // Pre-indexed
+ return ARM::LDRSB_PRE;
+ case 0: // Post-indexed
+ return ARM::LDRSB_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ case 15:
+ switch (PW) {
+ case 2: // Offset
+ return ARM::LDRSH;
+ case 3: // Pre-indexed
+ return ARM::LDRSH_PRE;
+ case 0: // Post-indexed
+ return ARM::LDRSH_POST;
+ default:
+ break; // fallthrough
+ }
+ break;
+ default:
+ break; // fallthrough
+ }
+ }
+
+AutoGenedDecoder:
+ // Calling the auto-generated decoder function.
+ return decodeInstruction(insn);
+}
+
+// Helper function for special case handling of LDR (literal) and friends.
+// See, for example, A6.3.7 Load word: Table A6-18 Load word.
+// See A8.6.57 T3, T4 & A8.6.60 T2 and friends for why we morphed the opcode
+// before returning it.
+static unsigned T2Morph2LoadLiteral(unsigned Opcode) {
+ switch (Opcode) {
+ default:
+ return Opcode; // Return unmorphed opcode.
+
+ case ARM::t2LDRDi8:
+ return ARM::t2LDRDpci;
+
+ case ARM::t2LDR_POST: case ARM::t2LDR_PRE:
+ case ARM::t2LDRi12: case ARM::t2LDRi8:
+ case ARM::t2LDRs: case ARM::t2LDRT:
+ return ARM::t2LDRpci;
+
+ case ARM::t2LDRB_POST: case ARM::t2LDRB_PRE:
+ case ARM::t2LDRBi12: case ARM::t2LDRBi8:
+ case ARM::t2LDRBs: case ARM::t2LDRBT:
+ return ARM::t2LDRBpci;
+
+ case ARM::t2LDRH_POST: case ARM::t2LDRH_PRE:
+ case ARM::t2LDRHi12: case ARM::t2LDRHi8:
+ case ARM::t2LDRHs: case ARM::t2LDRHT:
+ return ARM::t2LDRHpci;
+
+ case ARM::t2LDRSB_POST: case ARM::t2LDRSB_PRE:
+ case ARM::t2LDRSBi12: case ARM::t2LDRSBi8:
+ case ARM::t2LDRSBs: case ARM::t2LDRSBT:
+ return ARM::t2LDRSBpci;
+
+ case ARM::t2LDRSH_POST: case ARM::t2LDRSH_PRE:
+ case ARM::t2LDRSHi12: case ARM::t2LDRSHi8:
+ case ARM::t2LDRSHs: case ARM::t2LDRSHT:
+ return ARM::t2LDRSHpci;
+ }
+}
+
+/// decodeThumbSideEffect is a decorator function which can potentially twiddle
+/// the instruction or morph the returned opcode under Thumb2.
+///
+/// First it checks whether the insn is a NEON or VFP instr; if true, bit
+/// twiddling could be performed on insn to turn it into an ARM NEON/VFP
+/// equivalent instruction and decodeInstruction is called with the transformed
+/// insn.
+///
+/// Next, there is special handling for Load byte/halfword/word instruction by
+/// checking whether Rn=0b1111 and call T2Morph2LoadLiteral() on the decoded
+/// Thumb2 instruction. See comments below for further details.
+///
+/// Finally, one last check is made to see whether the insn is a NEON/VFP and
+/// decodeInstruction(insn) is invoked on the original insn.
+///
+/// Otherwise, decodeThumbInstruction is called with the original insn.
+static unsigned decodeThumbSideEffect(bool IsThumb2, uint32_t &insn) {
+ if (IsThumb2) {
+ uint16_t op1 = slice(insn, 28, 27);
+ uint16_t op2 = slice(insn, 26, 20);
+
+ // A6.3 32-bit Thumb instruction encoding
+ // Table A6-9 32-bit Thumb instruction encoding
+
+ // The coprocessor instructions of interest are transformed to their ARM
+ // equivalents.
+
+ // --------- Transform Begin Marker ---------
+ if ((op1 == 1 || op1 == 3) && slice(op2, 6, 4) == 7) {
+ // A7.4 Advanced SIMD data-processing instructions
+ // U bit of Thumb corresponds to Inst{24} of ARM.
+ uint16_t U = slice(op1, 1, 1);
+
+ // Inst{28-24} of ARM = {1,0,0,1,U};
+ uint16_t bits28_24 = 9 << 1 | U;
+ DEBUG(showBitVector(errs(), insn));
+ setSlice(insn, 28, 24, bits28_24);
+ return decodeInstruction(insn);
+ }
+
+ if (op1 == 3 && slice(op2, 6, 4) == 1 && slice(op2, 0, 0) == 0) {
+ // A7.7 Advanced SIMD element or structure load/store instructions
+ // Inst{27-24} of Thumb = 0b1001
+ // Inst{27-24} of ARM = 0b0100
+ DEBUG(showBitVector(errs(), insn));
+ setSlice(insn, 27, 24, 4);
+ return decodeInstruction(insn);
+ }
+ // --------- Transform End Marker ---------
+
+ // See, for example, A6.3.7 Load word: Table A6-18 Load word.
+ // See A8.6.57 T3, T4 & A8.6.60 T2 and friends for why we morphed the opcode
+ // before returning it to our caller.
+ if (op1 == 3 && slice(op2, 6, 5) == 0 && slice(op2, 0, 0) == 1
+ && slice(insn, 19, 16) == 15)
+ return T2Morph2LoadLiteral(decodeThumbInstruction(insn));
+
+ // One last check for NEON/VFP instructions.
+ if ((op1 == 1 || op1 == 3) && slice(op2, 6, 6) == 1)
+ return decodeInstruction(insn);
+
+ // Fall through.
+ }
+
+ return decodeThumbInstruction(insn);
+}
+
+static inline bool Thumb2PreloadOpcodeNoPCI(unsigned Opcode) {
+ switch (Opcode) {
+ default:
+ return false;
+ case ARM::t2PLDi12: case ARM::t2PLDi8:
+ case ARM::t2PLDr: case ARM::t2PLDs:
+ case ARM::t2PLDWi12: case ARM::t2PLDWi8:
+ case ARM::t2PLDWr: case ARM::t2PLDWs:
+ case ARM::t2PLIi12: case ARM::t2PLIi8:
+ case ARM::t2PLIr: case ARM::t2PLIs:
+ return true;
+ }
+}
+
+static inline unsigned T2Morph2Preload2PCI(unsigned Opcode) {
+ switch (Opcode) {
+ default:
+ return 0;
+ case ARM::t2PLDi12: case ARM::t2PLDi8:
+ case ARM::t2PLDr: case ARM::t2PLDs:
+ return ARM::t2PLDpci;
+ case ARM::t2PLDWi12: case ARM::t2PLDWi8:
+ case ARM::t2PLDWr: case ARM::t2PLDWs:
+ return ARM::t2PLDWpci;
+ case ARM::t2PLIi12: case ARM::t2PLIi8:
+ case ARM::t2PLIr: case ARM::t2PLIs:
+ return ARM::t2PLIpci;
+ }
+}
+
+//
+// Public interface for the disassembler
+//
+
+bool ARMDisassembler::getInstruction(MCInst &MI,
+ uint64_t &Size,
+ const MemoryObject &Region,
+ uint64_t Address,
+ raw_ostream &os) const {
+ // The machine instruction.
+ uint32_t insn;
+ uint8_t bytes[4];
+
+ // We want to read exactly 4 bytes of data.
+ if (Region.readBytes(Address, 4, (uint8_t*)bytes, NULL) == -1)
+ return false;
+
+ // Encoded as a small-endian 32-bit word in the stream.
+ insn = (bytes[3] << 24) |
+ (bytes[2] << 16) |
+ (bytes[1] << 8) |
+ (bytes[0] << 0);
+
+ unsigned Opcode = decodeARMInstruction(insn);
+ ARMFormat Format = ARMFormats[Opcode];
+ Size = 4;
+
+ DEBUG({
+ errs() << "Opcode=" << Opcode << " Name=" << ARMUtils::OpcodeName(Opcode)
+ << " Format=" << stringForARMFormat(Format) << '(' << (int)Format
+ << ")\n";
+ showBitVector(errs(), insn);
+ });
+
+ ARMBasicMCBuilder *Builder = CreateMCBuilder(Opcode, Format);
+ if (!Builder)
+ return false;
+
+ if (!Builder->Build(MI, insn))
+ return false;
+
+ delete Builder;
+
+ return true;
+}
+
+bool ThumbDisassembler::getInstruction(MCInst &MI,
+ uint64_t &Size,
+ const MemoryObject &Region,
+ uint64_t Address,
+ raw_ostream &os) const {
+ // The Thumb instruction stream is a sequence of halhwords.
+
+ // This represents the first halfword as well as the machine instruction
+ // passed to decodeThumbInstruction(). For 16-bit Thumb instruction, the top
+ // halfword of insn is 0x00 0x00; otherwise, the first halfword is moved to
+ // the top half followed by the second halfword.
+ uint32_t insn = 0;
+ // Possible second halfword.
+ uint16_t insn1 = 0;
+
+ // A6.1 Thumb instruction set encoding
+ //
+ // If bits [15:11] of the halfword being decoded take any of the following
+ // values, the halfword is the first halfword of a 32-bit instruction:
+ // o 0b11101
+ // o 0b11110
+ // o 0b11111.
+ //
+ // Otherwise, the halfword is a 16-bit instruction.
+
+ // Read 2 bytes of data first.
+ uint8_t bytes[2];
+ if (Region.readBytes(Address, 2, (uint8_t*)bytes, NULL) == -1)
+ return false;
+
+ // Encoded as a small-endian 16-bit halfword in the stream.
+ insn = (bytes[1] << 8) | bytes[0];
+ unsigned bits15_11 = slice(insn, 15, 11);
+ bool IsThumb2 = false;
+
+ // 32-bit instructions if the bits [15:11] of the halfword matches
+ // { 0b11101 /* 0x1D */, 0b11110 /* 0x1E */, ob11111 /* 0x1F */ }.
+ if (bits15_11 == 0x1D || bits15_11 == 0x1E || bits15_11 == 0x1F) {
+ IsThumb2 = true;
+ if (Region.readBytes(Address + 2, 2, (uint8_t*)bytes, NULL) == -1)
+ return false;
+ // Encoded as a small-endian 16-bit halfword in the stream.
+ insn1 = (bytes[1] << 8) | bytes[0];
+ insn = (insn << 16 | insn1);
+ }
+
+ // The insn could potentially be bit-twiddled in order to be decoded as an ARM
+ // NEON/VFP opcode. In such case, the modified insn is later disassembled as
+ // an ARM NEON/VFP instruction.
+ //
+ // This is a short term solution for lack of encoding bits specified for the
+ // Thumb2 NEON/VFP instructions. The long term solution could be adding some
+ // infrastructure to have each instruction support more than one encodings.
+ // Which encoding is used would be based on which subtarget the compiler/
+ // disassembler is working with at the time. This would allow the sharing of
+ // the NEON patterns between ARM and Thumb2, as well as potential greater
+ // sharing between the regular ARM instructions and the 32-bit wide Thumb2
+ // instructions as well.
+ unsigned Opcode = decodeThumbSideEffect(IsThumb2, insn);
+
+ // A8.6.117/119/120/121.
+ // PLD/PLDW/PLI instructions with Rn==15 is transformed to the pci variant.
+ if (Thumb2PreloadOpcodeNoPCI(Opcode) && slice(insn, 19, 16) == 15)
+ Opcode = T2Morph2Preload2PCI(Opcode);
+
+ ARMFormat Format = ARMFormats[Opcode];
+ Size = IsThumb2 ? 4 : 2;
+
+ DEBUG({
+ errs() << "Opcode=" << Opcode << " Name=" << ARMUtils::OpcodeName(Opcode)
+ << " Format=" << stringForARMFormat(Format) << '(' << (int)Format
+ << ")\n";
+ showBitVector(errs(), insn);
+ });
+
+ ARMBasicMCBuilder *Builder = CreateMCBuilder(Opcode, Format);
+ if (!Builder)
+ return false;
+
+ Builder->SetSession(const_cast<Session *>(&SO));
+
+ if (!Builder->Build(MI, insn))
+ return false;
+
+ delete Builder;
+
+ return true;
+}
+
+// A8.6.50
+// Valid return values are {1, 2, 3, 4}, with 0 signifying an error condition.
+static unsigned short CountITSize(unsigned ITMask) {
+ // First count the trailing zeros of the IT mask.
+ unsigned TZ = CountTrailingZeros_32(ITMask);
+ if (TZ > 3) {
+ DEBUG(errs() << "Encoding error: IT Mask '0000'");
+ return 0;
+ }
+ return (4 - TZ);
+}
+
+/// Init ITState. Note that at least one bit is always 1 in mask.
+bool Session::InitIT(unsigned short bits7_0) {
+ ITCounter = CountITSize(slice(bits7_0, 3, 0));
+ if (ITCounter == 0)
+ return false;
+
+ // A8.6.50 IT
+ unsigned short FirstCond = slice(bits7_0, 7, 4);
+ if (FirstCond == 0xF) {
+ DEBUG(errs() << "Encoding error: IT FirstCond '1111'");
+ return false;
+ }
+ if (FirstCond == 0xE && ITCounter != 1) {
+ DEBUG(errs() << "Encoding error: IT FirstCond '1110' && Mask != '1000'");
+ return false;
+ }
+
+ ITState = bits7_0;
+
+ return true;
+}
+
+/// Update ITState if necessary.
+void Session::UpdateIT() {
+ assert(ITCounter);
+ --ITCounter;
+ if (ITCounter == 0)
+ ITState = 0;
+ else {
+ unsigned short NewITState4_0 = slice(ITState, 4, 0) << 1;
+ setSlice(ITState, 4, 0, NewITState4_0);
+ }
+}
+
+static MCDisassembler *createARMDisassembler(const Target &T) {
+ return new ARMDisassembler;
+}
+
+static MCDisassembler *createThumbDisassembler(const Target &T) {
+ return new ThumbDisassembler;
+}
+
+extern "C" void LLVMInitializeARMDisassembler() {
+ // Register the disassembler.
+ TargetRegistry::RegisterMCDisassembler(TheARMTarget,
+ createARMDisassembler);
+ TargetRegistry::RegisterMCDisassembler(TheThumbTarget,
+ createThumbDisassembler);
+}
+
+EDInstInfo *ARMDisassembler::getEDInfo() const {
+ return instInfoARM;
+}
+
+EDInstInfo *ThumbDisassembler::getEDInfo() const {
+ return instInfoARM;
+}
generated by cgit v1.1 at 2025-01-07 20:51:07 +0000